Water tube boiler with upper and lower transverse drums



April 24, 1951 E. K. MOSIER ET AL 2,549,843

WATER TUBE BOILER WITH UPPER AND LOWER TRANSVERSE DRUMS Filed March 2'7, 1945 OOOOOOOOOOOOOOOO QOOOOOOOOQKOOOO BY A? ankX': Gi/g Patented Apr. 24, 1951 VVATEB, TUBE BOILER WITH UPPER AND LOWER TRANSVERSE DRUMS Edwin K. Mosier, Closter, and Frank X. Gilg, Chatham, N. J., assignors to The Babcook & Wilcox Company, Roclrleigh, N. 3., a corporation of New Jersey Application March 27, 1945, Serial No. 585,120 3 Claims. (01. 122 302) The present invention relates to water tube steam boilers and more particularly to bent tube, multiple drum boilers of the type specifically adapted for low dr ft loss service.

In many industries Where limited requirements of steam for power or process work exist, com bustibles or lay-products such as bagasse or hogged fuel, which might otherwise be considered waste, are burned in special furnaces to generate such steam. These fuels are usually of a high moisture content which introduces a problem of combustion and frequently a problem of disposal of the solid material carry-over from the furnace into the boiler. The carryover, such as in the burning of bagasse, may adhere to boiler heating surfaces in the form of relatively light weight, fiuffy masses of unburned combustibles and ash which will tend to plug any restricted gas passes occurring within the boiler. Often,

as in the case of th sugar-cane industry where tion through the heat absorbing tube banks, and

a reduction in this item has long been sought. It is economically desirable to accomplish the drafting of the boiler by the use of a natural draft stack or chimney which is of limited height, and

a draft loss through the boiler of less than .75 7 inch water gage is the desideratum.

It is the main object of the present invention toprovide a steam boiler unit of adequate heat transfer capacity which will have a characteristically low draft loss when operated at the designed normal rate of steam generation. A further and more specific object is to provide a boiler and furnace setting for burning high moisture solid fuels which will be of simple and co .1- pact design and of low construction cost. An additional object is to provide a boiler and associated furnace wherein a supplementary fuel,

such as oil, may be burned in conjunction with or in place of a high moisture fuel without involving an expensive boiler and furnace structure. Another object is to provide an arrangement of boiler heat absorbing surface having heating gas confining and directing walls which direct the gas in relatively high heat transfer contact with the boiler tubes while involving'a ill minimum of gas flow restrictions. An additional object is to provide a boiler unit with gas flow paths between the furnace and the stack outlet so positioned as to avoid abrupt directional changes in the heating gas flow, thereby resulting in a low boiler draft loss. Another object is to provide an arrangement of boiler tube banks which will encourage the separation of particles of ash and unburned combustibles from the heating gases for separate removal from the setting, while positioning the tube banks in the gas path so that the undue deposition of such particles on the heat transfer surfaces will be avoided, thus eliminating the need for soot blowing equipment.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawlugs and descriptive matter in which we have illustrated and described a preferred embodiment of our invention.

Of the drawings:

Fig. 1 is a sectional elevation of a steam boiler constructed in accordance with our invention as associated with a bagasse furnace; 1

Fig. 2 is a plan section of the boiler tube bank taken on the line 2- 2 of Fig. 1; and

Fig, 3 is a modification, in sectional elevation, of a portion of the boiler pressure parts.

The low draft los boiler of the present invention is illustrated in the drawings in association with a well known type of bagasse furnace, such as disclosed in U. S. Patent 2,114,619. While other types of furnaces suitable for other fuels having either a high or low moisture and ash content may be substituted for the bagassg burning furnace illustrated without adversely afiectingthe heat transfer efficiency and low draft loss characteristics of the boiler hereinafter described, the steam boiler construction hereinafter described is particularly designed and especially useful for the burning of bagasse and other high moisture fuels.

Referring to Fig. 1, the bagasse furnace l0 may be considered as divided into a lower hearth portion l I and an upper portion I2. The hearth portion is of internal elliptical horizontal crosssection with the vertical wall thereof merging into the walls of the upper portion which is'of rectangular cross-section. A multiplicity of slotted air ports 53 in the base and a plurality of vertically spaced rows of circumferentially spaced tuyeres E4 in the wall of the hearth section I l di- 3 rect the flow of combustion air into contact with the bagasse delivered thereto through a feed spout IS. The combustion air is delivered to the ports i3 and tuyere it through a series of communieating ducts, as at it, from a common air chamber i1 within a hollow bridge wall iii. Combustion air is supplied to the chamber il' through a port 20 at either end thereof at a pressure above atmospheric by an external fan (not shown) and serves to cool the bridge wall. The furnace side of the wall It defines the rear side of the furnace l while the opposite side of the furnace is defined by a vertical front wall 2! which extends upwardly to a horizontal refractory roof 22 forming a portion of the furnace and boiler setting. The rounded top of the bridge wall !8 ends at a position spaced from the roof 22, and, at an intermediate point above the hearth is provided with a suspended arch 23 which inclines upwardly toward the front wall 2i to define a throat 2e therebetween. The arch 23 is provided with a transversely arranged row of spaced tuyere blocks 25 which direct jets of air from chamber i! downwardly across the upper portion :2 of furnace Iii. Above the throat 25 the wall from the wall 2! to provide a diverging passage into an upper chamber 26.

Thus, bagasse or similar fuel deposited on the hearth through the spout i is burned with combustion air entering through the ports i3 and tuyeres l4 generating heating gases which are mixed with additional air from the tuyere blocks and pass upwardly through the throat 26 into the chamber 26. The burning of bagasse necessarily leaves a residue of ash or non-combustible refuse which is periodically removed from the hearth through a clean-out door 21. In addition, the furnace iii and chamber 26 are provided with a plurality of inspection port 23, while the air chamber is similarly provided with a clean-out and access door 30.

The boiler illustrated in Fig. l is of the multiple drum type having three upper steam and water drums 3|, 32 and 33 and a lower water drum 34 connected by banks 35 and 36 of upright tubes. The plurality of upper drums provides adequate steam separating space for the rating involved thus avoiding the necessity of complicated steam separating drum internals. The customary boiler arrangement having the two forward steam and water drums at one elevation and the rear steam off-take drum 33 at a slightly higher elevation is utilized, with interconnecting steam circulator tube 3'! and 38 and water circulator tubes 4s and 4 I, in the interest of high quality of the saturated steam delivered from the drum 33.

The tube bank 35 is positioned forwardly in the boiler and consists of transverse rows of tubes 82, 43, M and Q5, the tubes 42 and 43 being arranged and spaced to form a relatively widely spaced tube screen opposite the gas outlet from chamber 26, as illustrated in 2. The tubes enter the upper drum 3i and lower drum in three circumferentially spaced rows with the front tube rows t2 and i? having their end per tions in transverse alignment and entering the drums in the same row of tube openings. At the elevation of the chamber 25 outlet is thus provided two rows of staggered tube lengths having a transverse spacing of 12 in. or twice the transverse spacing at the drum connections. The spacing of the tube rows 32 and :3 at the center line of the chamber 255 outlet is of the order of 12 in. compared with a spacing of 6 in. between rows e3, 54 and 45 at the same elevation.

it inclines away Cal With such an arangement, the gases from the chamber pass in cross-flow relation across the screen tubes to give high heat transfer, while involving a low flow restriction and draft loss. The tubes of bank 35 are so arranged that individual tubes may be removed and replaced without disturbing the other tube of the bank, and without involving any displacement of the furnace structure, particularly the bridge Wall I8.

The lower portion of the tube bank 35 is spaced from the upper inclined rear face 48 of bridge wall it! so that any carry-over of solid particles which may be separated from the gas flowing through the tube bank will drop downwardly on the inclined face i's, which is maintained in relatively cool condition by the opposed rows of tubes of bank 35, and the particles will be deflected downwardly into the collecting chamber $2 from which they may be periodically removed through the cleanout door 68.

The hotter gases leaving the chamber 26 and passing through the screen bank 35 naturally hug the upper portion of the boiler setting and are directed by the lower exposed segments of the upper drum and the baffies Eli and El carried by the drum circulators iii and 4| into the upper rear portion of the setting through which the upright rear tube bank 35 extends. The rear bank 355 is made up of two groups of transverse rows of tubes connected at their lower ends to the top and rear quadrant segments of the lower drum 35, with the forward group consisting of eight rows having their upper ends connected to the bottom of the center drum 32 and the rearward group of four rows having their upper ends connected to the bottom of the rear drum 33. The tubes of the rear bank have the major portion of their lengths extending in an upright position in a closely spaced aligned tube row arrangement, as indicated in Fig. 2. The center to center spacing of the rows of these tubes, which are shown of 3% in O. D., is of the order of 4 in., while the transverse spacing of the tubes in each row is alternately 5 in. and 6% in. to permit removal and replacement of individual tubes. The upper portions of the forward group of eight tubes of the bank 38 are inclined so that their upper ends are 'ofiset from the upright intermediate tube portions and in their inclined portions have a greater row to row spacing.

A bafiie extends upwardly from the drum 34 between and supported by the first two tube rows of the bank 35, and with the setting rear wall 53 and side walls defines a downflow gas pass in which the lower portion of the tube bank 36 is located. Preferably the lower end of baffle 52 is spaced from the drum 36 to provide an opening 49 therebetween for a restricted flow of heating gases therethrough across the lower end of the tube bank 35. Such gas flow across the top of the drum 34 will prevent an accumulation of solid carryover materials at this location and further contribute to the self cleaning characteristic of the boiler. The tube bank 36 constitutes the principal convection heat absorbing surface of the boiler and it is so positioned with respect to the entering flow of heating gases the outfiow of cooled gases from the bottom of its downflow gas pass, that a low gas flow restriction and consequently a low draft loss results.

With the baffle 52 extending to an elevation somewhat above that of the top of the bridge wall is, the major portion and particularly the hotter gases leaving the front bank will flow in a horizontal direction from the chamber 26 and enter the bank=36 at its upper end. The gases enter the bank 36 flowing in a cross-tube relation and must thereafter change their direction to flow parallel with the tubes in the down pass over the major length thereof. The gas flow between the tubes at the entrance end of the bank 36 is subject to three flow restrictions, the entrance draft loss, the cross-tube flow draft loss, and the draft loss due to the change of direction.

In the boiler of the present invention these flow restrictions are maintained at a minimum by the arrangement and spacing of the tubes at the gas entrance end of bank 36. Heating gases entering a tube bank at an oblique angle to the axes of the tubes will tend to leave the tube bank in a direction normal to the tube axes. Thus, the heating gases entering the inclined upper portion of the tubes in the bank 36 will be diverted upwardly toward the roof of the setting and will avoid any tendency toward crowding of the gas through the forward tubes directly above the baffle 52. This will tend to produce a substantially uniform distribution of gases entering the tube bank and will provide a favorable condition for a low entrance draft loss. The diversion of heating gases upwardly toward the roof of the boiler setting will also advantageously assure an efiective utilization of the heat absorptive surfaces of the upper end of the tubes in bank 36 in the region of the drums 32 and 33.

While that portion of the gases entering the upper inclined section of the tube bank 36 is sub-- jected to a greater cross tube flow restriction than the gases entering the tube bank immediately above the upper end of baffie 52, due to the increased spacing of the tube rows, such loss will be largely compensated by an accompanying lower turning loss due to lower gas velocities in the wider back tube row spacings. The combined effect of such tube row spacin and tube inclination will tend to maintain an equalized distribution of the gases and low draft losses in flowing through the portion of the tube bank between the baffle 52 and the rear wall 53.

At the bottom of the gas pass 59 where the cooled gases leave the lower portion of bank 36, a flue gas outlet 54 is positioned in the rear wall at an elevation approximating the level of the lower drum 34. The front to back width of the gas pass is increased by the forwardly bent lower portion of the front tube rows and baffle 52, as well as by the inclined wall face 55 so that a low flow resistance will result in the gases turning from downflo to horizontal flow in passing through the spaces between the lower bent ends of the tubes of bank 36 and into the rearing chambers ii and 56, and prevents the bypassing of heating gases beneath the drum 34.

The height of the baffle 52 above the lower drum 34 is selected to provide a suitable gas pass opening between the upper end thereof and the drum 32 so as to obtain a low draft loss con- 6 sistent with a desirable heat transfer rate between the heating gases and the boiler heating surfaces. A decreased height of the baffle will decrease the draft losses through the boiler, but will also reduce the heat transfer rate. However, the height of the baffle, within optimum limits of from approximately /3 to /3 of the total vertical spacing between the drums 34 .and 32 will have a relatively small effect upon the draft loss and a lesser effect upon the heat transfer rate of the boiler unit. For example, at a boiler rating of 175% and with the baflle 52 extended upwardly to its optimum upper limit the draft loss will be of the order of .75 in. water, while at its optimum lower limit the draft loss will be approximately .65 in. water. The accompanying change in heat transfer rate would also decrease with the draft loss, but in a lesser proportion. At this boiler rating the unit is capable of burning approximately 2 /2 pounds of bagasse per hour per square foot of boiler heating surface at an efficiency comparable with that of boiler units having twice the draft loss therethrough. Expressed in figures applicable to other fuels the 2 /2 pounds of bagasse is equivalent to approximately 13.6 pounds of heating gase per hour per square foot of boiler heating surface passing through the boiler, and with the heating gases entering the boiler at a temperature of approximately 1800" F.

Advantageously, an oil burner at is installed within a port 52 in the vertical front wall 2| at a central location with respect to the chamber 26. Such a burner may be operated during idle periods of the bagasse furnace or, when desired, to supplement the burning of bagasse. Moreover, this arrangement permits an inexpensive wall construction and the use of a minimum floor area for the boiler and furnace while providing a suitable combustion volume for burning both the bagasse and oil.

A modification of the boiler front tube bank is shown in Fig. 3 wherein the relative tube spacing within that tube bank is maintained substantially as shown in Figs. 1 and 2, with however an increase in the spacing between the forward row of tubes in bank 36 and the tube row of the front tube As shown, the ro of tubes 43 occupy the position of the row of tubes 42 in Fig. 1 while the remaining tubes 42', 44 and 45' are bent near their drum connections to be displaced substantially as shown.

If desired in the installation of the steam generating equipment a superheater may be inserted in the space between the front and rear tube banks. A suitable type of superheater is shown in Fig. 1 wherein a superheater inlet header 63 is connected with the boiler steam drum 33 by a series of tubes 54. A series of inverted U-shaped superheater tubes 65 connect the header 63 with an outlet header 56. As shown, the headers 63 and 63 are protected by a refractory tile 61 across the tops thereof and the assembly is supported in the proper position by clips 33 attached to the adjacent rows of tubes in the front and rear tube banks. The superheated steam temperature required from the steam generating unit described may, in some installations be greater than that shown in Fig. 1. Under such conditions the modifled arrangement of the front tube bank shown in Fig. 3 may be advantageously used to provide a larger space for superheating surface.

We claim:

1. A steam generating unit having a setting, means defining a furnace chamber occupying the 7 rent portion of said setting and including a vertically extending bridge wall separating said furnace chamber from the rear portion of said setting and spaced from the top of said setting to define a gas outlet therebetween, steam generating pressure parts in the rear portion of said setting including front, middle and rear upper drums, a lower drum, a front bank of vertically extending screen tubes connecting said front upper drum and lower drum and arranged adjacent the rear side of said bridge wall, a rear bank of vertically extending steam generating tubes connecting said lower drum to said middle and rear upper drums, said rear tube bank having the tube upper and lower end portions in the tube rows in at least the forward portion thereof bent forwardly of and more widely spaced than the intermediate tube portions of said rows, a baffle extending upwardly from said lower drum along the forward side of said rear tube bank and terminating at an intermediate position between said lower and upper drums, said baffle and setting cooperating to define a heating gas entrance into and heating gas flow transversely of the upper portion of said rear tube bank and a dowrflow gas pass containing the lower portion of said rear tube bank, ash receiving chambers below said front and rear tube bank, and a heating gas outlet from said setting adjacent said lower drum.

2. In combination, walls defining a steam boiler setting, a furnace chamber occupying the lower front portion of said setting, a vertically extending bridge wall separating said furnace chamber from the rear portion of said setting and spaced from the top of said setting to define a horizontal gas pass therebetween, the upper furnace side of said bridge wall inclining toward the front wall of said setting to define a vertical gas pass therebetween, an oil burner in the upper portion of the front wall of said setting, a steam boiler in the rear portion of said setting including front, intermediate and rear upper drums and a lower drum, a front bank of vertically extending tubes connecting said front upper drum with said lower drum, the lower portion thereof arranged adjacent the rear side of said bridge wall, a rear bank of vertically extending tubes connecting said intermediate and rear upper drums with said lower drum, said rear tube bank having the tube upper and lower end portions in the tube rows in at least the forward rows thereof bent forwardly of and more widely spaced than the intermediate portions of said tube rows, a bafiie extending upwardly from a spaced position above said lower drum along the forward side of said rear tube bank and terminating at a spaced position between said upper and lower drums, said baffle and setting cooperating to direct a generally horizontal flow of heating gas into the upper portion of said rear tube bank and a downflow of heating gas through the lower portion of saidv rear tube bank, and a flue connection in said setting adjacent said lower drum.

3. A steam generating unit having a setting, a steam boiler within said setting having upper and lower drums, a front bank of vertically extending steam generating tubes connecting said upper and lower drums, a rear bank of vertically extending tubes spaced from said front bank and connecting said upper and lower drums, said rear tube bank having the tube upper and lower end portions in the tube rows in at least the forward rows thereof bent forwardly of and more widely spaced than the intermediate portions of said tube rows, and means for passing heating gases through said tube banks at a high heat transfer rate and a low draft loss which comprises means for directing a flow of heating gases to the upper portion of said front tube bank in a generally horizontal direction normal to the axes of said tubes,

a bafile extending upwardly from said lower drum along the forward side of said rear tube bank and terminating at a spaced position between said upper and lower drums, said baffle and setting cooperating with the upper end portions of said rear bank of tubes to direct a substantially uniformly distributed and horizontal flow of heating gases into the upper portion of said rear tube bank and to direct a substantially uniformly distributed downflow of gases through the lower portion of said bank, and a gas outlet from said setting adjacent said lower drum.

EDWIN K. IWOSIER. FRANK X. GILG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,726,050 Ward Aug. 27, 1929 2,058,043 Smith Oct. 20, 1936 2,244,451 Falla June 3, 1941 2,313,251 Marshall Mar. 9, 1943 FOREIGN PATENTS Number Country Date 4,384 Great Britain Feb. 20, 1913 197,877 Great Britain May 24, 1923 519,789 Germany Mar. 4, 1931 

